From my inbox: 1, 2, 3-tube radios, cheap cap tester, cheap frequency synthesizer

  • Build a radio with three tubes or less. This article lists radios that you can build with three tubes or fewer. In general, this is a very cool website. (Thanks to Brad, AA1IP, and the Glowbugs mailing list.)
  • Cheap capacitance tester. The Glowbugs mailing list also recently had a discussion of cheap capacitance testers. I just bought a fancy, new Keithley DMM  that measures capacitance, but some of the instruments mentioned in this thread also measure inductance. The consensus seems to be that while they’re not as accurate as a “real” test instrument, for $20 or so, how can you go wrong?Brad, AA1IP mentions the article, “A Low Cost Automatic Impedance Bridge” by Dr. George Steber, WB9LIV, that appeared in the October 2005 QST. Brad says, “This arrangement uses a PC’s sound ports, a dual-section op amp, a few components and some software to deliver reasonably precise RLC measurements along with a graphic screen display.”
These frequency-synthesizer boards use the AD9850, and can be purchased on eBay for as little as $5 each.

These frequency-synthesizer boards use the AD9850, and can be purchased on eBay for as little as $5 each.


  • Cheap AD9850 boards. The AMRAD mailing list has a thread on these inexpensive signal-generator modules. One of the AMRAD guys has been experimenting with using them with an Arduino to make frequency control easier. They’re only $5 each and generate 0 – 40 MHz.On the Glowbugs list, they talked a little bit about these boards, too. One guy gave a link to the article, “An Improved VFO Driver Amp for Tube Rigs.” This article describes a circuit that allows you to easily use the AD9850 boards (or any other digital synthesizer, for that matter) as the VFO for a tube rig.


  1. Dave, N8SBE says:

    AADE sells a capacitance/inductance meter, either assembled or as a kit —

    I got my AADE LC meter from Bill, N8ET, who runs Kanga US, out of Findlay, OH —

    I just went to the Kanga site, and found this notice:

    IMPORTANT NOTICE: Bill (N8ET) had a stroke in mid-March 2013.
    Kanga US operations are temporarily on hold, until Bill recovers.

    I’m shocked. Bill is a young guy (compared to us old geezers). My thoughts and prayers go out to him and his family, and I’m hoping for a quick and complete recovery. I’ve met and chatted with Bill many times over the previous several years at local hamfests and at Dayton.

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